%I A001231
%S A001231 1,1,1,1,0,1,1,4,0
%N A001231 Number of nonisomorphic projective planes of order n.
%C A001231 The Bruck-Ryser theorem says that a(n)=0 if n == 1 or 2 (mod 4) and is 
               not the sum of two squares.
%D A001231 CRC Handbook of Combinatorial Designs, 1996, p. 695.
%D A001231 Handbook of Combinatorics, North-Holland '95, p. 672.
%D A001231 C. W. H. Lam, The Search for a Finite Projective Plane of Order 10, American 
               Mathematical Monthly, 98, (no. 4) 1991, 305 - 318.
%D A001231 C. W. H. Lam, G. Kolesova and S. Swiercz, A computer search for finite 
               projective planes of order 9, Discrete Math., 92 (1991), 187-195.
%D A001231 C. W. H. Lam, L. Thiel and S. Swiercz, The non-existence of finite projective 
               planes of order 10, Canad. J. Math., 41 (1989), 1117-1123.
%H A001231 C. W. H. Lam, <a href="http://www.cecm.sfu.ca/organics/papers/lam/index.html">
               Publications</a>
%H A001231 Ed Pegg, Jr., <a href="http://www.mathpuzzle.com">Finite affines planes 
               of low orders</a>
%H A001231 N. J. A. Sloane, <a href="http://www.research.att.com/~njas/doc/sg.txt">
               My favorite integer sequences</a>, in Sequences and their Applications 
               (Proceedings of SETA '98).
%H A001231 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               ProjectivePlane.html">Projective Planes</a>
%Y A001231 Sequence in context: A058473 A115527 A050920 this_sequence A141150 A089418 
               A124856
%Y A001231 Adjacent sequences: A001228 A001229 A001230 this_sequence A001232 A001233 
               A001234
%K A001231 nonn,hard,nice
%O A001231 2,8
%A A001231 N. J. A. Sloane (njas(AT)research.att.com).